The objective of this research is to develop non-invasive electrophysiological techniques to investigate and evaluate the peripheral and central pathways of the trigeminal nerve and to apply these techniques to dental disorders such as trigeminal nerve injury. This proposal will focus on potentials recorded on the scalp in response to electrical stimulation of the trigeminal nerve. The first specific aim is to identify the scalp location and the latency of the potential which represents the (1) initial cortical response to electrical stimulation of the trigeminal nerve by simultaneously recording from multiple scalp electrodes and comparing amplitudes to exclude short-latency potentials arising from subcortical structures. The second, third, and fourth specific aims will investigate the possible contamination of scalp potentials by myogenic signals. Specifically, the hypotheses that potentials evoked by electrical stimulation of the trigeminal nerve and recorded on the scalp over the somatosensory cortex include (2) masticatory muscle, (3) facial muscle, or (4) cervical muscle potentials elicited by jaw opening or jaw closing reflexes, trigemino-facial reflexes, or trigemino-cervical reflexes by identifying the latencies and origins of these muscle potentials, if any, in the waveforms recorded on the scalp. Utilizing the information gained in the first four objectives, the fifth specific aim will investigate the (5) clinical utility of trigeminal evoked potentials by comparing the amplitude of the trigeminal evoked potentials and the nerve integrity of a group of patients with injury to the mandibular branch of the trigeminal nerve. This specific aim will identify latencies of the potentials which are altered in amplitude as specific clinical signs and symptoms of nerve integrity change over time.